Method of manufacturing arsenate of lead.



EDWIN 0. BARSTO'W, 0F YIDLAND, MICHIGAN, ASSIGNOR TO THE 130 CHEMICAL COMPANY, OI MIDLAND, MICHIGAN, A CORPORATION 6F MICHIGAN.

METHOD OF MANUFACTURING A ItSENATE OF LEAD.

Ho Drawing.

'a citizen of the United States, and a resident of Midland, county of Midland, and State of Michigan, have invented a new and useful Improvement in Methods of Manufacturing Arsenate of Lead, of which the following is a specification, the principle of the invention being herein explained. and the best mode in which I have contemplated ap plying that principle, so as to distinguish it from other inventions.

The present method or process may be regarded as a n'iodification of the general process of manufacturing lead arsenate presented in my co-pending application filed even date herewith and since issued into Patout No. 1,169,114, dated January 25 1916.

In this case, as in such general process, the mode of procedure involved is equally ap plicable to the manufacture of other in soluble arsenates than lead arsenate, as for example, zinc, iron and barium arsenates.

The process constituting the present invention, then, consists of the steps hereinafter fully described, and particularly pointed out in the claims.

The following description sets forth in detail one approved modcof carryingoutthe in vention, such disclosed mode, however, being merely illustrative of the various ways in which the principle of the invention may be used.

The general method of procedure involved in the improved process under consideration consists in oxidizing an arsenic derivative to arsenic acid by means of a halogen; providing a compound to form a haloid with such halogen reagent; and adding a suitable compound of the metal, the arsenate of which is desired as a final product. As previously indicated, the process is applicable to any metal capable of being precipitated as such arsenate from its corresponding solublesalt,

such its haloid. Commenting further on.

this statement relative to the general mode of procedure, it should he noted that it is immaterial so far as the steps in the process are concerned, whether they be performed 'in the sequence just indicated, or in part or in whole, simultaneously; and, as will now be explained, in the present modification of such general process, the base for forming a haloid with the halogen reagent is added first, and the halogen for oxid ziig the Specificaiion of Letters Patent,

Patented May 23, 1916.

Application filed August 1, 1912. V Serial No. 712,677.

arsenic derivative is added subsequently. In carrying out such )IOCQSS, white arsenic, or arsenius oxid (As is dissolved in a solu tion of soda ash, or equivalent alkali, and, inasmuch as no carbonic acid gas is apparently evolved, the reaction would seem to be correctly represented by the following equation The exact intermediate phenomena, however, are immaterial both here and in such other reactions as may be indicated subsequently; it being the end result of course that is of interest. The next step in the process is to chlorinate the solution thus obtained, as a result of which a solution of arsenic acid and common salt may for convenience in representation be assumed to be obtained, as exhibited by the following react1on':r-, QNaH,AsO +2NaHCO -l-2H O+4Cl:

Although it proljiable that arsenic acid, hydrochloric acid, sodium arsenate and sodium chlorid are all present, as well as free ions of sodium, chlorin and the arsenate radical, AsO

\Vhere, as in the specific instance assumed for illustrative purposes, it is lead arsenate that is wanted, the oxid of this metal is then stirred into the solution. The reaction occurring may be represented as follows, assum ing the signification reagent solution to be arsenic acid 2H,AsO,+4-la(lll-2Pb02 Instead of the lead oxid, the hydrate, carbonate, or basic carbonate of lead may be used as per the following reactions Preferably, the amount of soda ash used in preliminary forming the sodium arsenite, is somewhat greater than the actual requirements of the chlorin subsequently added. Conversely the amount of lead oxid,

or other lead compound, that added, will preferably be less than an equivalent of the free acid in the solution.

As an alternative to the reactions given above to represent what happens When the sodium arsenite is chlorinated, and an oxygen derivative of lead thereupon added to the resulting solution, the following equations are given z- It is immaterial, so far'as the reaction with the lead oxid is concerned, Whether arsenic acid, or hydrochloric acid, or both, be assumed to be present; and in determining the amount of such oXid to be added, it suffices to determine the amount of free acid present without inquiring as to Whether it is one or the other.

The mixture obtained by the last described step is next dropped onto a filter and washed with water leaving the lead arsenate, which is chiefly the acid lead arsenatc behind. The filtrate and washings, containing sodium chlorid, sodium arsenate and free acid are, however, saved, and so dium carbonate is added thereto, until the acid is at least neutralized. Finally lead chlorid solution is run in to precipitate the normal lead arsenate, Pb (AsO,) the reaction for which be thus represented steps. Such reaction is, however. presented here as a part of the general process only.

The i'n'elimiuary reaction, that of treating arsenious oxid with soda ash may be conducted satisfactorily in an open tank or tub into which these materials, together w ith water are charged; while the chlorination will be conducted in stone-Ware, cokemcked chlorination towers, the mixture to be chlorinated being pumped continuously over v aid towers. The lead oxid, or equiva lent oxygen derivative of the metal of whi h the arscnatc desired, is added to the solution of arsenic acid and sodium oXid in a wooden tank provided with a suitable stirrer, the solution being sull'iciently concentrated to provide av mixture of the proper consistency. It has been discovered that by ulli-cicntly prolonging the stirring, th lead arscuutc ma made from the solid lead oXid, hydrate, carbonate, or basic carbonate, despite the fact that, at first sight, it would seem that this reaction could not be carried to completion, because the resulting product being solid, the lead oXid would not be reacted upon, but particles of it would be inclosed in an impervious coating of the lead arsenatc. On subjecting the liquid, however, to a suiliciently prolonged this tendency hasstirring. or agitation, been successfully overcome as above indi cated.

The oxygen derivatives of lead, which are suitable for use as compounds of that metal for reacting with arsenic acid to form lead arsenate, have already been indicated. The term oxygen derivative is intended, therefore, to connote such equivalents of lead oxid in addition to those which have been specifically named, as will fcrmthe compound in question under the conditions surrounding the reaction. By way of general comment, it should further be noted that both the acid lead arsenate PbllAsO,, and the normal arsenate Pb,(,\s(),),, are commonly known to the trade as arsenate of lead. The latter term is accordingly to be understood as used herein in this general sense, and not as referring specifically to either of the two arsenatcs named except Where the contrary is indicated. So, too, a soluble alkaline earth arscnate may be used instead of the alkaline arsenate hercinbe fore specified, as the preferred soluble article, as will be readily understood, rind such equivalent is intended to be connoted by the term alkaline as herein employed.

It is proper to repeat, way i'gf 'conclusion, that the several equations which have been heretofore referred to as the different reactions involved, are presented as illustrative, merely of the principal phenomena. They do not, however, necessarily represent all of the reactions that actually occur, and should be understood as indicating how the desired cndproduct is derived, rather than the exact intermediate steps leading thereto. From the standpoint of the nmnufacturer or practical chemist, indeed, it might be better to represent the whole series of detailed reactions pcrtaining to each particular process or subprocess described above, as a single comprehensive reactii'in, in which only the starting materials and observed end-products are given. Thus, for example, the specific mode of operation herein claimed may be represented as tollows:-

As,O ,+2Na,()(),,+4Cl+H O+2PbO:

' 2PbHAsQ,+4NaCl-l-2H,O. In other words, so far operation ot the process in hand is con ccrncd, it may be regarded as consisting in a reaction between white arsenic, soda ash,

as the commercial expressive of chlorin and lead oxid. As has already been indicated, the present process limit l to solu in: that specific aspect of the general reaction soluiion on on described, in which soda ash if; 0 m :n' nptwi toproiluce mined with the white arsenic to form 'oinble arsenite before the chlorination 5% Other modes of applying principle oi my invention. may be employed instead of the one explained, change h T regards the process herein vided the slap oi steps state of the following claims or ii such stnteel step or steps he I therefor-e particularly point on tinctly slain: as my inven1ion1-- l. The method of making an. insolnble metallic arsenate, which con sts in treat ing a solution of an arsenate W th a halogen; and adding to such treated solution a, bompouncl of the metal of which the arsenate is desired, such compound being adapted to produce sneh zLI'SQIlfiiO upon being added to a solution of. ilfSeUlC acid.

2. The method of maki metallic iii-senate, Will-oh in the presenee of we :3 he l'bfilllhlllg; ei'ivam'e of the is deal msenious to form a eel. rimming 3 ing :olution which the pound being adapted to pi'oduce such d! e net-e upon being aimed to a solution of on senic acid. i

The method of making an insoluble metallic arsenate, which consists in the pres anon of W L with chlorin; and {'1 1 h of an oxid of the nni'i'ei naite is desired.

4:. The meilm'i which r issue in Water, an reacting, with t oxygen Cifif'lVz (luce such an: in

of Water an (i, and reacting an oxygen 02 dnoe lead tonsiss '7 of Mite, an and reacting with the lead oxid.

7 The. method of mak ng lead e2 napi which consists in tr n soluiiini of SUCI'HIH) arsenite with chic-rm; and then stirring ihe resulting solniion with lead 0206..

S. The

We of arsenals the steps which consist in stirring adapted to produce such arsenate upon being added to a solution of arsenic acid, whereby the acid arsenate of said metal is obtained, the amount of such ox i gen derivative bcin insufficient to combine with all the free acid present; separating out such arscnate; adding an alkali to the residual solution; and then adding a solution of the chlorid of said metal thereto.

15' In a method of making an insoluble metallic zirsenatc, the steps which consist in. stirring :1 solution of arsenic acid With the oxid of the n'ietal of which the arsenatc .is desired, whereby the .arsenate of said metal is obtained, the amount of such oxid being insutlicicnt to combine with all of the acid present; filtering out such arsenato; adding sodium carbonate to the filtrate; and then adding a solution of the chlorid of said metal thereto.

16. In a method of making lead arscnate, a solution with lead oxid, whereby amount of arsenic acid acid lead iii-senate is obtained, the of such oxid being insufficient to with all of the acid present; separating out such arsenate; adding an alkali to the residual solution; and then adding lead ch10- rid solution thereto.

17. In a method of making lead arsenate, the steps which consist in stirringasolution of arsenic acid with lead oxid, whereby acid lead arsenate is obtained, the amount of such oxid being insutiiizient to combine with all the free acid present; filtering out such arsenate; adding sodium carbonate to the filtrate; and then adding lead chlorid solution thereto.

Signed by me this 27th day of July, 1912.

-IJDW IN 0. BARSTOVV;

Attested by A. N. PATRIARCHE, LEO W. Lows.

combine 

